Personally I believe in using what you have. I doubt there's any filter so much better than your existing one as to justify its cost. Realistically it's unlikely you'll max out your biological filtration capacity, and if you need more flow powerheads are much more versatile and far less expensive. I would suggest adding an intake sponge of some sort; it's probably the best filtration upgrade you can make.
Lighting diffuser is a common choice for exactly that purpose and should be readily available at your local hardware store. You don't have to be very exact with the size or shape, especially since the stuff is a pain to cut.